In a large number of cases, it is required to read an image from a disc and modify it in a "one dimensional" manner, that is for example, to create a new "red" content purely as a function of the existing red image. Thus, data is read from a bulk storage device, such as a magnetic hard disc or an optical disc, and under the control of a Central Processing Unit (CPU) is routed through a data table stored in RAM (Random Access Memory) which is in the CPU's memory map. This results in modified data which, in itself, may probably undergo further modifications. A conventional system uses a disc controller which includes a data buffer and communicates with the remainder of the system via a SCSI or other interface.